I have a diverse range of music and the existing search feature works well with all of my music except for classical music.  In classical music, the composer is of a great deal of interest, as is the conductor, soloist, and orchestra.  When I rip classical music, I include both the performer and the composer with the hope that I can index searches with either one.

Adding a composer field to the search would be a significant improvement for those of us who enjoy classical music.  It would also be interesting for other music affectionados who have an interest in the music performers we like have written but did not record (there are a number of great examples of this, such as Carole King and Randy Newman -- to name a couple).